Annals of African Medicine

ORIGINAL ARTICLE
Year
: 2009  |  Volume : 8  |  Issue : 2  |  Page : 110--114

Intrapair birthweight discordance in twins


Alphonsus N Onyiriuka 
 Department of Child Health, University of Benin Teaching Hospital, P.M.B 1111, Benin City, Nigeria

Correspondence Address:
Alphonsus N Onyiriuka
University of Benin Teaching Hospital, P.M.B 1111, Benin City
Nigeria

Abstract

Background : Birthweight differences in twin pairs influence their perinatal outcome as well as growth and development. Growth-discordant twins have not been well characterized in our local environment. Objective : To determine the frequency of birthweight discordance in live-born twin pairs and document some factors that may influence it. Methods : In this cross-sectional study, 104 live-born twin pairs were recruited and their intrapair birthweight differences were determined. Twin pairs whose birthweight difference was 15% or more, using the larger infant as the growth standard, were designated as discordant. The maternal age, parity, and birth order of the heavier twin were noted. Results : The prevalence of birthweight discordance was 28.8% when a 15% cut-off point was used but dropped to 9.6% when a 25% cut-off point was applied. Grand multiparity was associated with a significantly increased risk of delivery of discordant twins. Same-sex twin pairs accounted for 60% of all cases of birthweight discordance. Conclusion : Birthweight discordance is common in twin gestations in Benin City, especially among grand multiparous women.



How to cite this article:
Onyiriuka AN. Intrapair birthweight discordance in twins.Ann Afr Med 2009;8:110-114


How to cite this URL:
Onyiriuka AN. Intrapair birthweight discordance in twins. Ann Afr Med [serial online] 2009 [cited 2020 Sep 21 ];8:110-114
Available from: http://www.annalsafrmed.org/text.asp?2009/8/2/110/56239


Full Text

 Introduction



Birthweight discordance is a common growth problem in twin gestations, with varying frequency depending on the definition used. [1] The threshold for clinically significant discordance has been variably defined as 15% [1],[2] and 25%, [3] respectively. Using a birthweight difference of more than 25% as a cut-off point, Blickstein et al, compared two cohorts of twin pairs, one from four different perinatal centers (United States, Poland, and two from Israel) and the other from a Swedish population-based data; they found birthweight discordance of 11% in the former and 12% in the latter. [3] Some investigators have reported that divergent fetal growth increases the risk of fetal death [2],[4],[5] and other adverse outcomes such as prematurity [4],[6] with its attendant morbidity and mortality. In a study of 122 live-born twin pairs delivered between 25- and 34-week gestation, Cheung et al.[7] reported that birthweight discordance greater than 30% was associated with congenital anomalies and complications of prematurity. Both physical and intellectual follow-up examinations have shown that a discordant twin was at a disadvantage. [8]

In view of the potential adverse outcomes that may be associated with the phenomenon of growth discordance in twins, participants of an international census survey recommended that every twin gestation should be evaluated for growth discordance and, when diagnosed, should be observed very closely. [9]

Growth-discordant twins have not been well characterized in our local environment. In fact, there are statements in the literature indicating that even in developed countries growth-discordant twins are poorly characterized, [1],[4] suggesting global paucity of information on the subject.

The present study sought to determine the frequency of birthweight discordance in twin gestations in Benin City and document some of the factors that may influence it.

 Materials and Methods



This descriptive (cross-sectional) study was conducted in a Nigerian mission hospital in Benin City. The hospital, St. Philomena Catholic Hospital (SPCH), has a large maternity unit with an average of 1,344 deliveries annually. [10]

During the 4-year study period January 1, 2000 to December 31, 2003 all twin babies delivered at SPCH were weighed naked by a trained midwife, within the first 30 min after birth, using a rotational balance made by Waymaster, England, and calibrated to the nearest 50 g. This scale was checked periodically with known weights for reliability and daily for zero error to ensure accuracy. The weights, birth order, and sexes of the babies as well as their corresponding maternal ages and parity were recorded.

In the present study, a twin pair was designated discordant if one of the pairs was smaller by 15% or more. The level of discordance was calculated for each pair as a percentage of the birthweight of the heavier twin [discordance (%) = 100 (birthweight difference/birthweight of heavier twin)]. Intrapair birth-weight percentage differences were stratified into the following categories: 15-24.9%, 25-34.9%, and 35% or more, which roughly corresponded to moderate, severe, and extreme discordance, respectively. The percentage difference in birthweight of t-test for mean and Z-test for proportions with the level of significance set at P Z-statistic = 0.515; P > 0.05. Comparing the mean birthweight of discordant-first and discordant-second pairs, it was 1973 g (95% confidence interval, CI = 1753-2193) versus 2312 g (95% CI = 2090-2534); t = 2.123; P > 0.05. When the birthweight difference was more than 500 g, the greater would be the likelihood that the smaller twin would be second-born.

[Table 1] showed that the incidence of birthweight discordance was 1.9 times higher in the year 2003 compared to the year 2000 (P > 0.05). The frequency of birthweight discordance in twins appeared not to be influenced by maternal age [Table 2]. As shown in [Table 3], grand multiparous mothers were at a significantly increased risk of delivery of growth-discordant twins compared to multiparous mothers (P P > 0.05).

Comparing grand multiparous women with their multiparous counterparts, there was a 3-fold increase in the risk of occurrence of the moderate level of birthweight discordance in the former [Table 6] P > 0.05. The risk of the moderate level of birthweight discordance was 1.5 times higher in grand multiparous women compared to their primiparous counterparts P > 0.05.

 Discussion



The present study further confirms the report of a previous study [1] that the frequency of birthweight discordance in twin gestation depends on the definition used. For instance, the prevalence of twin pairs with birthweight discordance was 28.8% when 15% cut-off point was used but dropped to 9.6% when 25% cut-off point was applied. The prevalence (28.8%) reported here is higher than the 16.9% reported from Israel by Blickstein et al, [1] using the same 15% cut-off point, suggesting a higher prevalence among Nigerian twins. The reason for this difference in prevalence is not clear. It is possible that the high incidence of anemia in pregnancy and chronic malnutrition in developing countries, [11] may result in lower combined twin birthweight among Nigerian mothers compared to their Israeli counterparts. It has been shown that the lower the combined twin birthweight, the higher the frequency of delivery of birthweight-discordant twins. [3],[12] On the other hand, when 25% cut-off point was applied, our frequency (9.6%) compared favorably with 9.3% reported by Ekure and Iroha [16] in Lagos, Nigeria. Further comparison was not possible because the authors of the Lagos study did not state the prevalence using 15% as a cut-off point.

Data from the present study indicated that the risk of delivery of growth-discordant twin pairs was significantly higher in grand multiparous women compared to their multiparous counterparts. Primiparous mothers also tended to deliver growth-discordant twins more often than their multiparous counterparts, although the difference did not reach statistical significance. Similar findings have been reported by other investigators. [12],[13],[14] From this finding, it would appear that the uteri of multiparous women were more efficient in nurturing twins compared to those of their primiparous counterparts. As a consequence, multiparous women were more likely to deliver larger twins with higher combined twin birthweight. This is in keeping with the report of Blickstein et al, [3],[15] which showed that the higher the combined twin birthweight the less likely it was to deliver discordant pairs. In that report, they stated that the uteri that can efficiently nurture twins are associated with increased combined twin birthweight and decreased discordant frequencies. [15] In the case of grand multiparous women, it is possible that the higher number of previous deliveries, especially if in quick succession, may have exhausted these women nutritionally leading to intrauterine malnutrition and hence lower combined twin birthweight. As a consequence, the risk of delivery of birthweight-discordant infants is increased. A previous study in the same hospital had shown that the frequency of delivery of low birthweight infants by grand multiparous women was relatively high. [17] Although same-sex twin pairs accounted for 60% of all cases of birthweight discordance, the difference was not statistically significant. Other investigators [3],[18] have reported similar higher frequency of discordance in same-sex twin pairs, suggesting that birthweight in females may be influenced by a male co-twin, resulting in decreased frequency of intrapair birthweight discordance in different-sexed twin pairs. In this regard, Rydhstroem [19] reported that fetal loss was two times higher in the same-sex compared to different-sex twin pairs and only in the same-sexed pairs was fetal loss significantly correlated with birthweight discordance. The clinical implication was that discordance was more important to fetal well-being in the same-sex than in different-sex twin pairs. The present study indicated that more discordant-second pair was associated with the larger birthweight difference (more than 500 g). Similar findings have been reported by other investigators, [20] suggesting that the larger the weight disparity, the greater the likelihood that the smaller twin will be second born. It would, therefore, appear that the birth order of the heavier twin was an integral part of the discordance phenomenon. Although several investigators [20],[21],[22] have shown that first-born twins were not always heavier than their second-born siblings, data from the present study suggested that second-born twins have only 1.2 times the risk of being the lighter baby when there is at least 25% discordance between twin pairs. There is no readily available explanation for this finding.

In conclusion, birthweight discordance is common in twin gestations in Benin City, especially among grand multiparous women. It is, therefore, recommended that all twin gestations, particularly in grand multiparous women, should be evaluated for growth discordance and when diagnosed should be observed closely. Prevention of pregnancy in grand multiparous women, using family-planning methods, is advocated.

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